2-D imaging systems typically involve an illumination means and an imaging array, such as Complimentary Metal on Silicon (“CMOS”) or a Charge Coupled Device (“CCD”). Such systems use LEDs or other means to illuminate the object to be captured, and the light reflected from such object is then incident upon the imaging matrix. One problem associated with such devices is that the depth of field over which the illumination of the object can be kept constant is relatively narrow. For example, FIG. 1 shows how the intensity of illumination falls off drastically as a function of distance from the source.
In the prior art, solutions to this problem typically involve installing an additional one or more LEDs or other illumination means, which is directed to the area close to the device. One such arrangement is disclosed in U.S. Published Application No. 2006-0219792. In the '792 publication, two modes of operation are used, each of which has its own associated set of LEDs. Depending upon whether it is desired to capture images in the near field or far field, a different mode of operation is selected, which results in a different set of LEDs being illuminated. However, the position of the various LEDs, renders this arrangement somewhat less than optimal.
Another prior art arrangement with a separate set of LEDs to illuminate an area close to the imaging array is disclosed in U.S. Published Application No. 2006-0118627. As depicted in FIGS. 2A and 2B of the present application, which are taken from the referenced publication, showing a device having a housing 20, folding mirror 44, two illumination systems 42A and 42B, and imager 40. Illumination system 42A includes a plurality of LEDs exteriorly arranged on housing 20 around window 18. Each exterior LED projects light over a conical volume, shown as region 56A and 56B. The second illumination system 42B includes one or more LEDs disposed in housing 20 remote from window 18. The LEDs of system 42B project light over conical volume 58. In this fashion, system 42A illuminates a near range field-of-view and system 42B illuminates a far-range field-of-view, a separate set of LEDs is disposed vertically to the remaining circuit board in the device, and light is directed from these LEDs to illuminate the close in field of view.
These and other prior art arrangements are all suboptimal in that they require arrangements that are either too large in size, too expensive to manufacture, or which are cumbersome to use. Many involve positioning the source of secondary illumination in a manner that increases the manufacturing cost of the device.
Some such prior art arrangements are also less than optimal because the illumination means are positioned in a manner that may shine into a user's eyes. Thus, there exists a need in the art for an improved device that can provide for uniform illumination over a wide range of distances from the imaging array.